Aseries of enzymes catalyze the reaction x → y → z → a. product a binds to the enzyme that converts x to y at a position remote from its active site. this binding decreases the activity of the enzyme. with respect to the enzyme that converts x to y, substance a functions as?

The correct answer is: An allosteric inhibitor.

An allosteric inhibitor is the regulator of an enzyme that binds at a site other than the enzyme's active site. That site is called the allosteric site or regulatory site.

When the regulator binds enzyme usually goes through conformational change. Since the activity of the enzyme in example is reduced, we call it inhibitor, otherwise it would be activator.

The inhibition shown in example is negative feedback (final product turns off the reaction in the initial site).  

1: most common garden plants prefer loam — soils with a balance of different-sized mineral particles (approximately 40% sand, 40% silt, and 20% clay) with ample organic matter and pore space. however, some plants grow better in sandy soils, while others are well-adapted to clay soils.

2: available water capacity is the maximum amount of plant available water a soil can provide. it is an indicator of a soil's ability to retain water and make it sufficiently available for plant use. available water capacity is the water held in soil between its field capacity and permanent wilting point.

3: it is the same for all living things (plants and animals). it also includes very tiny organisms that our eyes cannot see. they are known as microorganisms, and include viruses, bacteria and fungi.